System for processing signal data to obtain improved contour presentations on a cathode-ray display

ABSTRACT

A system for processing analog signals representative of a parameter such as charge intensity, etc., along a scanned surface in contour mapping fashion. Monopolar and bipolar pulse patterns and a staircase signal are generated wherein the pulse spacing and staircase individual step widths are representative of corresponding input analog signal slopes at the corresponding points in real time. A variety of display intensity modulation signals is developed to permit a selection of contour presentations.

United States Patent Flemming [54] SYSTEM FOR PROCESSING SIGNALAssignee:

DATA TO OBTAIN IMPROVED CATHODE-RAY DISPLAY Inventor:

sex, England London, England Filed:

Appl. No.:

July 7, 1969 Foreign Application Priority Data John Peter WilfredFlemming, Harlow, Es-

Standard Telephones and Cables Llmited,

[451 Apr. 25, 1972 References Cited UNITED STATES PATENTS 3,473,08210/1969 Kolodnyckij ..315/30 [57] ABSTRACT A system for processinganalog signals representative of a parameter such as charge intensity,etc., along a scanned surface in contour mapping fashion. Monopolar andbipolar pulse patterns and a staircase signal are generated wherein thepulse spacing and staircase individual step widths are representativeJuly 10, 1968 Great Britain ..32,909/68 ofconesponding input analogsignal Slopes at he correspond ing points in real time. A variety ofdisplay intensity modula- U.S.Cl ..315/30,3l5/22 ion signals isdeveloped to permit a. selection of contour Int. Cl. .......H0lj 29/70presentations Field of Search ..3l5/30, 22; 181/.5 BE; 340/15 7 Claims,2 Drawing Figures [York Fri/ e r/ws/m/o 2 Detectors 3 r F Q Tif lDecoder /8 j/ 0/ fi fi- 8/nar Luff-fine (oz/0%! 2, /5 awe/9170b! 0/ PM?Adz/a [CI an er- I5 l V I? III (RT /n/m s/ty/ Contra/$417415 fat/min;

Analog Patented April 25,1972 I 3,559,144

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SYSTEM FOR PROCESSING SIGNAL DATA TO OBTAIN IMPROVED CONTOURPRESENTATIONS ON A CATHODE-RAY DISPLAY CROSS-REFERENCE TO RELATEDAPPLICATIONS This application is filed under the provisions of 35 U.S.C.l 19 with claim for the benefit of the filing of an application coveringthe same invention filed July 10, 1968 Ser. No. 32909/68 in GreatBritain.

BACKGROUND OF THE INVENTION 1. Field ofthe Invention This inventionrelates .to cathode-ray displays of scanned information and moreparticularly to systems for processing analog intensity modulationsignals for said displays.

2. Description of the Prior Art In the prior art, the presentation ofintensity modulated cathode-ray display patterns has been awidely usedexpedient for depicting variable amplitude analog signals resulting fromthe scan of a surface to be examined, such as by a scanning electronmicroscope or similar device.

One more specific example involves the generation of varying potentialsresulting from scan (as by a raster type scan, for example) ,of asemi-conductor surface having a potential or work function condition anddistribution to be investigated. A cathode-ray display used to presentthese data would be equipped with a raster scan synchronous with thatscanning of the electron microscope beam over the said semi-conductorsurface. In general, prior art systems applied the analog varyingamplitude signals thus obtained more or less directly as intensitycontrol signals to an intensity controlling element of the cathode-raydisplay. Biasing, d.c. level shifting andamplification were sometimesapplied, however the signals were applied otherwise unmodified.

One basic requirement of-a display of data from sources such as theaforementioned, is that it provide the observer with an image that isreadily interpreted. Another important requirement is that it shouldallow quantitative recovery of measuring system outputs.

Practically, the first requirement is met by careful attention to scanlinearity and correspondence between coordinates observed in thepick-up" scan and those of the display.

The second requirement is not met by direct application of theaforementioned intensity modulation analog signal, since recovery ofdiscrete 2" coordinate values is difficult. The unique method andapparatus of the present invention provides for the availability ofthese 2" coordinate values by encoding the said analog signal indiscrete steps in the circuit path before it is displayed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustratinga typical instrumentation of the device of the present invention.

FIG. 2 is a plot of various waveforms occurring during operation atvarious points in the device ofFIG. 1.

SUMMARY OF THE INVENTION In view of the indicated state of the prior artand its disadvantages, it was the general object of the presentinvention to generate several different types of 2" (intensitymodulation signals) for the selective presentation of the basic analogsignal data in various forms resembling contour relief maps.

According to the invention, there is provided an electrical arrangementfor processing an analog signal of the character described, for displayon a cathode-ray tube display device.

The structure includes a dual input summing amplifier, to one input ofwhich the analog signal is fed. The output of this amplifier is'appliedin parallel to upper and lower threshold detectors. Whenever the upperthreshold is attained by the signal at this point, a reversible counteris stepped once in one direction and once in' the other direction for alower threshold attainment. A decoder responds to both of said counterout- DESCRIPTION OF THE PREFERRED EMBODIMENT In describing the inventionwith respect to FIG. 1, reference will be repeatedly made to wavefonnsof FIG. 2. It is to be understood that a waveform called out withreference to an identifying letter is the corresponding waveform of FIG.2. The common abscissa of FIG. 2 is the sweep position of the scanningbeam (of an electron microscope. for example) providing the basic analogdata such as shown in waveform a. The abscissa could, in the case of alinear raster type scan, also be considered a (real) time base in theordinary sense.

In FIG. 1, the element 2 comprises the summing amplifier, and as such,includes the series resistors at inputs 1A and 1B, and also the feedbackresistor across the straight-forward differential type operationalamplifier l8 operated as a single variable input device with its otherinput grounded. The inputs at IA and 1B are seen to add at point 19 andthus the entire subcombination constitutes the said summing amplifier.

In this explanation a simple sine wave is taken as an assumed analogsignal input (waveform a) into terminal 1A. That wavefonn may, ashereinbefore indicated, have been generated by an electron microscopescanning a surface charge pattern, although it could have resulted fromany other scanning operation wherein the data is amenable topresentation as contour data on a synchronously scanned cathode-ray tubedisplay device.

The 13 input to the summing amplifier 2 is reserved in this case forintroduction of feedback as will be hereinafter understood. It will benoted that this feedback (or reference signal) is also provided to anoutput terminal 13. The precise nature of the said reference signal(waveform b) and its generation will be more fully described and will beapparent as this description proceeds.

The output of the summing amplifier 2 is provided to an output terminal14 as waveform c and in parallel to a pair of threshold detectors 3 and4. These elements 3 and 4 are identified as upper and lower thresholddetectors respectively. As the name implies, each is a circuit adaptedto deliver a trigger at any time that its input attains itspredetermined threshold. Various relaxation oscillators suitably biasedor offset are available in the art for instrumentation of thisparticular function.

The analog signal input at 1A is inverted by the summing amplifier 2, sothat, as the amplitude of the input signal falls, there is a rise in theoutput until the threshold level of detector 3 is attained and the saidtrigger is delivered via the synchronizing circuit 5 to the reversiblebinary counter 6.

Operation of the detector 3 causes the counter 6 to be advanced one stepin aforward direction at a rate determined by pulses from a clock pulsegenerator 7. Actually the pulses from detector 3 (and in the oppositepolarity from detector 4 as will be seen subsequently) are enablingpulses to the counter 6, the actual change of state being effected byclock pulses from 7 on line 23 via the gate 9.

Synchronizing circuit 5 is actually a logic type of circuit producing aninhibit control on lead 8 to the gate 9 to prevent "clock pulses on 23from operating the counter during any time than during the occurrence ofany clock pulse.

The counter output is fed to adecoder 10, which is actually adigital-toanalog converter for generating the reversible staircase"(waveform b) at a level such that when this signal is fed back to the IBinput of 2, the level of the output signal from 2 is reduced to a levelintermediate that of the threshold levels of the two detectors 3 and 4.Waveform 6 graphically conveys this summing amplifier signalrelationship. The upper and lower threshold levels are shown in dottedline in connection with waveform c.

Considering now the sequence resulting from lower threshold triggeringfrom 4, an opposite process occurs, with counter 6 being stepped once inreverse direction upon each attainment of the said lower threshold levelof detector 4.

Therefore, during operation, a stepped reference voltage (waveform b) issubtracted from or added to the input signal within 2, the amplifiedalgebraic difference or sum at the amplifier output is thereby keptwithin limits set by the said threshold detectors. See again the outputof 2 at waveform c.

Referring now specifically to the four output terminals 11, 12, 13 and14, the four varieties of cathode-ray device intensity modulatingsignals available may be summarized.

Terminal 11 provides the waveform f, which is actually the flip-flop"signal of the first (least significant) stage of the counter 6 (waveformd) via the differentiator l6 and the rectifier 15. Afterdifferentiation, the counter output is converted to waveform e, andrectification at 15 results in the waveform f 2 5 as aforesaid atterminal 11. It may be said that successive changes of state of thefirst counter stage (which are the same whether the counter is steppedforward or backward) are available in leading edge form at terminal 11.

Terminal 12 will be seen to provide the mixed outputs of the thresholddetectors 3 and 4 via the pulse adder 17. As previously indicated, oneof the lines 20 or 21 will convey positive trigge'r pulses and the othernegative pulses. Thus, after addition in 17, the waveform g is obtainedat terminal 12. The significance of the two polarities of intensifyingpulses will be more fully understood as this description proceeds.

Terminal [4 provides the waveform c, and terminal 13 the feedback(reference) signal of waveform b previously discussed.

In view of this available selection of cathode-ray display intensitycontrol signals, four modes of system operation will be seen to follow.These modes are arbitrarily identified as modes A through D, as follows:

Mode A: By using the output from terminal I l (waveform f) as anintensity modulation function in a raster scanned system, the contoursgenerated with gradient line much like in elevation contour mapping. Thegranularity of the contours (spacing of individual illuminations) willdepend on the number of scan lines employed per unit of physicaldimension, according to well understood principles.

Mode B: In this mode, the bipolar intensity pulses of waveform g areemployed to inject the increasing and decreasing slope concept into thepresentation. Thus, not only more, but also less intensified successivemarking points are presented. The observer may interpret the resultingdisplay by supposing that a light shines over the contoured surface,being scanned and displayed, in the direction of scan and is reflectedor casts a shadow depending on the sign of the incremental slope of thevariable with respect to the direction of scan. This produces anillusion of three dimensionality and can be helpful in interpreting theparameter distribution on the scanned surface unambiguously.

Mode C: In this mode, the output from terminal 13 (waveform b) isemployed as the intensity function. The advantage of this mode ofdisplay over the prior art direct intensity modulation (by the analogsignal of scanned surface parameter variation) technique is that thestepped (discontinuous) changes in brightness enables the observer toappreciate progressive change of brightness (instantaneous value ofparameter presented) without calibration equipment.

Mode D: By using the upper and lower threshold limited summary amplifieroutput (waveform 0) available from terminal 14 as the intensifyingfunction, the result is a display of a contour map in which thebackground brightness is controlled by details of the way the signalchanges between discrete contour points or levels. This mode of displayhas the effect of providing improved tone quality of the display sincethe transition from light to dark (display dynamic range) needcorrespond only to a change in signal value of one contour level ratherthan to a relatively large peak-to-peak amplitude range of theintensifying function (as in waveform b, for example).

It will be realized that various modifications in the instrumentationillustrated could be made within the spirit of the in vention. Also,displays provided in accordance with the described modes could becombined. That is, Mode A intensity signals might be combined with afraction of the Mode D signals, thereby afiording some of the advantageof each. The drawings and description herein are illustrative only andnot intended to be limiting as to the scope of the invention.

What is claimed is: V s

1. A device for processing electrical analog signals representative ofthe distribution of a parameter over said processing to adapt saidanalog signals for application as intensity controlling signals for acorrespondingly scanned cathode-ray display device, comprising:

Summing means for accepting said analog signal and also a referencesignal as inputs, to produce an output which is a continuous algebraicsum of said analog and reference signals;

Threshold detection means connected to said summing means output forproviding a trigger pulse, of a first polarity whenever said outputincreases by a predetermined threshold amount, and a second polaritywhenever said output decreases by a second predetermined thresholdamount;

Clock means for generating a series of equally spaced clock pulses of afrequency high with respect to the frequency of said analog signals;

A reversible binary counter responsive to said clock pulses and to saidtrigger pulses to advance by one step during each of said trigger pulsesof said first polarity and to reverse by one step during each of saidtrigger pulses of second polarity;

A digital-to-analog decoder connected to receive the output digitalwords of said counter to operateas a staircase generator havingindividual steps which are each the analog of a corresponding value ofsaid digital word, thereby to produce said reference signal;

And means connecting said reference signal to said summing amplifier,thereby to produce a closed loop circuit having a plurality of signalpoints therein each providing a corresponding discrete form of saidintensity control signals.

2. The invention set forth in claim 1 in which said threshold detectionmeans includes upper and lower threshold detectors fed in parallel fromsaid summing means for developing said trigger pulses of first andsecond polarity respectively.

3. The invention set forth in claim 1 in which said reference signal isprovided to an output terminal as a cathode-ray device intensity controlsignal.

4. The invention set forth in claim 1 in which the output of saidsumming amplifier is supplied to an output terminal as a cathode-raydevice intensity control signal.

5. The invention defined in claim 2, further defined in that there isincluded a pulse adder connected to add said pulses of first and secondpolarity, and means are included to supply the output of said pulseadder to an output terminal as a cathoderay device intensity controlsignal.

6. The invention set forth in' claim 1 in which counter operated meansare included for deriving and supplying to an to provide saidcathode-ray device intensity control signal in unipolar form.

1. A device for processing electrical analog signals representative ofthe distribution of a parameter over said processing to adapt saidanalog signals for application as intensity controlling signals for acorrespondingly scanned cathode-ray display device, comprising: Summingmeans for accepting said analog signal and also a reference signal asinputs, to produce an output which is a continuous algebraic sum of saidanalog and reference signals; Threshold detection means connected tosaid summing means output for providing a trigger pulse, of a firstpolarity whenever said output increases by a predetermined thresholdamount, and a second polarity whenever said output decreases by a secondpredetermined threshold amount; Clock means for generating a series ofequally spaced clock pulses of a frequency high with respect to thefrequency of said analog signals; A reversible binary counter responsiveto said clock pulses and to said trigger pulses to advance by one stepduring each of said trigger pulses of said first polarity and to reverseby one step during each of said trigger pulses of second polarity; Adigital-to-analog decoder connected to receive the output digital wordsof said counter to operate as a staircase generator having individualsteps which are each the analog of a corresponding value of said digitalword, thereby to produce said reference signal; And means connectingsaid reference signal to said summing amplifier, thereby to produce aclosed loop circuit having a plurality of signal points therein eachproviding a corresponding discrete form of said intensity controlsignals.
 2. The invention set forth in claim 1 in which said thresholddetection means includes upper and lower threshold detectors fed inparallel from said summing means for developing said trigger pulses offirst and second polarity respectively.
 3. The invention set forth inclaim 1 in which said reference signal is provided to an output terminalas a cathode-ray device intensity control signal.
 4. The invention setforth in claim 1 in which the output of said summing amplifier issupplied to an output terminal as a cathode-ray device intensity controlsignal.
 5. The invention defined in claim 2, further defined in thatthere is included a pulse adder connected to add said pulses of firstand second polarity, and means are included to supply the output of saidpulse adder to an output terminal as a cathode-ray device intensitycontrol signal.
 6. The invention set forth in claim 1 in which counteroperated means are included for deriving and supplying to an outputterminal, a signal representative in time of the change of state of theleast significant stages of said counter, as a cathode-ray deviceintensity control signal.
 7. The invention defined in claim 6 in whichsaid counter operated means includes a differentiator connected to thebistable signal of said first stage and a rectifier is connected betweensaid differentiator and said output terminal, thereby to provide saidcathode-ray device intensity control signal in unipolar form.